One of my friends is running their program. He ruined a transmission using an Edge product and went with these guys upon replacing the transmission. He seems VERY pleased.
Mine sounds different inside the cab, but it is not annoying. The turbo whistle in the 2004's is much less than the 2003's due to the turbo changes. It is fairly "throaty" from 2000RPM and up.
I have not noticed the low end problems that the 2003 owners have described. I'm not sure what the difference is. My truck performs very similar to my 1999 7.3 from a stop.